The horror genre's most memorable monsters and villains have names. And, frequently, fully fleshed out identities and backstories. Viewers sometimes even see pictures of them when they were little, before they turned bad. Their faces—whether cloaked with a thick curtain of wet, black hair or dappled with leathery burn scars—inspire uneasy sleep. We empathize with them. We know what makes them angry, why they kill, and sometimes, how to stop them.

But not in It Follows. The deliriously frightening new low-budget horror film by David Robert Mitchell bucks the genre's habit of over-explaining monsters by going in the exact opposite direction—revealing nothing. The premise is deceptively simple: Girl meets boy. Boy and girl have sex. Boy tells girl (surprise!) he just gave her a curse: A mysterious creature in the form of a person will follow her until it kills her, unless she has sex with another person and passes the curse along to them. But if that person dies, the creature will come after her again.

There's plenty to parse without wandering into the thick weeds of the film's (inadvertently) daunting sexual politics. The unwitting curse-bearer, 19-year-old Jay (Maika Monroe), spends the entire film running from "it" with the help of her sister and friends in the Detroit suburbs. "It" is a mindless, shapeshifting creature whose only mission is to silently stalk its victim to the death. The only other details: It walks slowly but never stops, it cannot be deceived, and it can look like a stranger or someone you know. Oh, and don't let it touch you.

The familiarity of the film's tropes belies the subtly radical spirit of It Follows. Rather than openly mocking and then transcending the genre's conventions, like the fantastic Cabin in the Woods, this film seems to tinker with horror's very DNA. On one level, It Follows seems like a comfortable albeit fresh reshuffling of horror-movie components (sex-as-deadly-sin, a gang of teenage friends teaming up to stop an evil force, scary house chases, a dark-and-stormy night scene). But step back, and it becomes clear just how unorthodox the film is: There are no dream sequences and no hallucinations. No real attempt to unravel the story of "it." No ghosts, no psychotics. Sex means death, but it also can mean life. There's very little gore and few jump scares. It's also got a not-quite-ironic intellectual touch to it: Large chunks of T.S. Eliot's poem The Love Song of J. Alfred Prufrock are recited aloud. And another character—a Hipster Ariel doppelganger, with big glasses, reddish hair, and a seashell Kindle-type device—reads from Fyodor Dostoevsky's The Idiot periodically.

But what's most satisfying about It Follows is how its monster manages to inspire such slow-burn terror when it spends 90 percent of the film doing something decidedly un-scary: walking slowly, often out of frame. Even the absence of the linearly traveling, unrelenting "it" is no relief: The anticipation of its arrival slowly and brutally wears the audience down, like death by a billion spoon thwacks. It's hard to know what to call the thing at the center of It Follows—a spirit? A monster? A villain? Is it even really evil or just a human embodiment of inhuman malevolence? As the director, Mitchell, has said: "There's no logic to it—you can't really explain a nightmare."

The inclination of horror movies to explain and profile the dark force as much as possible often results in a didacticism that doesn't translate well onscreen. Just think of how many films feature a haggard, wide-eyed protagonist poring through old texts, newspaper clippings, or Internet searches, or tracking down old victims in hopes of finding an answer. The process of the investigation itself can be spooky. The little girl was pushed into the well by her mom? Shudder. Rather than cultivating fear in the gradual, deliberate reveal of gruesome details, It Follows' thrust comes instead from training the audience to recoil from the shadowy, blurry figure on the horizon, behind the characters, without fanfare or warning.

The most obvious analogue for "it" is Stephen King's It, which is also a shapeshifting creature. But that monster diverges sharply from the one in It Follows in that it has a famous manifestation (as a very recognizable clown) and plenty of backstory (feeds every 30 years or so, prefers eating children). Even The Conjuring, another recent horror movie widely considered to be a new classic of the genre, dove into the history of the angry spirit that lived in the haunted house. It also spawned a spinoff based on the creepy doll whose face opens the movie: Annabelle. But It Follows does just fine without a famous face at its center.

Outside the horror film genre, J.K. Rowling (among others) understood that by suppressing a name from being spoken, fear could more easily take root, and that terror feeds on the undefined and unarticulated. Say Voldemort's name out loud, and it diminishes his power a little. And so the "it" of It Follows, robbed of even a proper noun and often referred to just as "this thing," only grows more powerful as the story progresses toward its hauntingly ambiguous end. For all the breakthroughs of the low-budget horror genre, It Follows represents a compelling evolution in how studios and audiences can (and should) conceive of its monsters.

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Lenika Cruz is a senior associate editor at The Atlantic, where she covers culture.